Plant pathogens are known to cause massive damage to important crops, resulting in significant agricultural losses with widespread consequences for both the food supply and other industries that rely on plant materials. As such, there is a long felt need to reduce the incidence and/or impact of agricultural pests on crop production.
Soybean rust (SBR), which is caused by the obligate fungal pathogen Phakopsora pachyrhizi H. Sydow & Sydow, was first reported in Japan in 1902. By 1934, the pathogen was reported in several other Asian countries and in Australia. More recently, P. pachyrhizi infection has been reported in Africa, and has spread rapidly through the African continent.
In November 2004, P. pachyrhizi was first reported in the continental U.S., and the pathogen has now been reported in more than 300 U.S. counties, in Canada, and in Mexico. In 2007, approximately 0.5 million hectares of soybean were sprayed for SBR control in the U.S.
SBR has the potential to cause significant yield losses in the U.S., as indicated by fungicide trials in Georgia and Florida that reported yield losses of 30 to 33% in untreated control plots. In Brazil, the total yield loss in the 2006-2007 growing season due to SBR was estimated to be over U.S. $2.26 billion with an average of 2.3 fungicide applications required per season. Yield losses up to 80% have been reported due to severe outbreaks of SBR, which result in early leaf drop that inhibits pod set. Consistent economic losses in Brazil over the last several years due to severe SBR outbreaks have raised concerns regarding the potential impact of this disease in the United States. Soybean cultivars currently available commercially in the United States are all susceptible to SBR to some degree, and fungicide applications are currently employed to control the disease.
Therefore, soybean rust resistant cultivars are needed to reduce fungicide costs and yield losses due to SBR.